Cannabis smoking may increase risk of lung cancer

Friday 19 September 2014 12:57pm

Associate Professor Brian Cox

University of Otago researchers have contributed to evidence that cannabis smoking may increase the risk of lung cancer in heavy users.

An international collaborative study of the International Lung Cancer Consortium, involving the Hugh Adam Cancer Epidemiology Unit of the University of Otago and the Medical Research Institute of New Zealand, assessed the risk of lung cancer from cannabis use. The New Zealand component of the study was funded by the New Zealand Ministry of Health and the Hawkes Bay Medical Research Foundation.

The study, published in the International Journal of Cancer, and which projected the effects of heavy use, suggested that heavy cannabis smoking for 20 or more years may increase the risk of lung cancer. The risk in heavy users was greatest for a specific type of lung cancer, adenocarcinoma of the lung.

A 40-year follow-up study of Swedish military recruits has also found a two-fold increase in the risk of lung cancer from heavy cannabis use. Both studies were adjusted for cigarette smoking, but this may have still contributed to the results obtained.

The studies suggest that more than the equivalent of one joint every two days for twenty years may increase the risk of lung cancer.

The University of Otago’s Associate Professor Brian Cox, who worked on the international study, says, "Compared to other countries, New Zealand has a high prevalence of cannabis use and this may increase the incidence of lung cancer in long-term users. Any risk of lung cancer increases progressively with increasing life-time use of cannabis."

“These findings are consistent with previous observations that smoking cannabis has a similar mixture of toxic products of combustion as cigarette smoking and that higher concentrations are likely to deposit in the lung due to cannabis smokers breathing in the smoke more deeply, and holding their breath longer. Our high rates of cannabis use indicate that we need to closely monitor the effects of cannabis use on respiratory diseases”, he says.

He added that the findings from these two studies suggest that public health programmes to reduce smoking may need to include greater initiatives to reduce cannabis smoking and need to be directed particularly at young people.

“Without support for effective intervention, the frequency of respiratory diseases caused by cannabis can be expected to increase in the near future as users get older. It should be no surprise that cannabis smoking may cause lung cancer and, due to our high prevalence of cannabis use, this risk needs to be more accurately assessed in New Zealand.”

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